Wood Protection Bulletin

Document Sample
Wood Protection Bulletin Powered By Docstoc
					                                            Wood Protection Bulletin
                                                                               Western Division
Canada’s National Wood
Products Research Institute                                                                        July 2003




         Properties of Lumber with Beetle-Transmitted Bluestain

Users of lumber are probably familiar with bluestain. Some may wonder if the amount and
type of stain transmitted by the mountain pine beetle affects the wood in any way. Compre-
hensive testing recently confirmed that beetle-transmitted bluestain has no practical effect
on strength properties or gluing characteristics. Neither does the bluestain affect the adhe-
sion of furniture finishes. The stain causes some possibly beneficial changes to dimensional
                              stability, checking and permeability.

R   egular customers for western spruce-pine-fir lumber have probably seen some bluestain, a subtle
streaking in the lumber. At the moment, bluestain is more prevalent than in the past, because British
Columbia is currently experiencing a large natural outbreak of mountain pine beetle (MPB). Native to
the forests of western North America, the MPB attacks several species of pine trees, including ones
commonly used for construction lumber and panels. The beetle carries with it a staining fungus that
weakens the tree’s defences which allows the insect to lay eggs under the bark.

While the beetle stays just under the bark, the fungus can grow throughout the sapwood (the outer
                                          part of the tree) feeding on sugars, carbohydrates and other
                                            nutrients contained within the wood cells. As the fungus
                                             spreads, it leaves behind a permanent blue or grey stain
                                              that colours products made from this wood. Neither the
                                               beetle nor the fungus eats the wood structure itself.

                                                 Bluestain fungi are not mold, nor do they cause
                                                  decay (rot) problems. They are considered harm-
                                                   less with respect to both wood products and peo-
                                                    ple, and are typically dead by the time the wood
                                                     products leave the manufacturer. The wood
                                                      can be handled exactly as with non-bluestained
                                                        wood. Because it looks slightly different,
                                                         questions are sometimes asked about
                                                          bluestained wood. Forintek performed a series
                                                           of tests to address any possible marketplace
                                                            concerns and to provide a scientific
                                                              basis for the anecdotal evidence that
                                                               bluestained wood is equivalent to non-
                                                                bluestained wood.




Eastern Division                                                                             Western Division
319, rue Franquet, Sainte-Foy, QC G1P 4R4                              2665 East Mall, Vancouver, BC V6T 1W5
Tel: (418) 659-2647                                                                        Tel: (604) 224-3221
Fax: (418) 659-2922                                                                       Fax: (604) 222-5690
                                            www.forintek.ca
   Property
    Tested                         Results                                Implications


Stiffness and       No significant difference.              These are the most important strength
breaking strength                                           properties for structural applications.
                                                            Bluestained wood is as strong and as stiff as
                                                            non-bluestained wood.


Impact resistance   Slightly lower (5%) impact              Toughness is not a critical strength
(toughness)         resistance for bluestain.               property for most end-uses of wood but
                                                            is one of the first properties affected
                                                            by biological agents.

                                                            The small reduction is much lower than
                                                            previously reported for other types of
                                                            wood and staining fungi and is of no
                                                            practical significance in construction.

Truss plate grip    Measurable (6%) increase in             Good plate grip capacity is critical for the
capacity            ultimate grip capacity but similar      design and manufacture of trusses. The
                    slip for bluestained wood as for non-   measured increase is not of practical
                    stained wood.                           significance for truss design.


Dimensional         Bluestained wood was significantly      Bluestained wood seems to develop
stability and       less prone to warping when tested in    micro-checks (hairline cracks). This may
checking (in        our simulation of outdoor exposure.     have implications for kiln-drying practices, as
repeated wetting/   Cracks were significantly smaller in    well as potential benefit for the appearance
drying)             bluestained wood.                       and performance of wood in outdoor use.
                                                            True outdoor testing is needed to clarify the
                                                            implications.




                                                               Bluestained lumber may be a good
                                                               candidate for decking material.
    Property
     Tested                          Results                                    Implications


Permeability and       Bluestained sapwood wets more              Bluestained sapwood is more easily treated
treatability with      readily with water. The heartwood          with wood preservatives and fire retardants.
preservatives          resistance to treatment is unchanged.
                                                                  Note that the green tint of many preservatives
                                                                  reduces the colour contrast between
                                                                  bluestained and non-bluestained wood.

                                                                  The combined benefits of bluestain-masking,
                                                                  increased treatability and improved checking
                                                                  appearance indicate that bluestained lumber
                                                                  heavy-to-sapwood is probably a good choice
                                                                  for treated decking products.

                                                                  Increased permeability may have implications
                                                                  for air or kiln drying—bluestained wood may
                                                                  dry faster.




Glue joint integrity   No difference between bluestained and      No changes required for use of either
                       non-bluestained wood in joint durability   structural or non-structural adhesives with
                       and strength.                              bluestained wood.




Finishes for           Best masking of bluestain for furniture    Furniture manufacturers could use
masking bluestain      grade products is achieved with stains,    combinations of these tints to reduce the
                       toners or glazes containing blue, red or   colour contrast between bluestained and non-
                       charcoal tints.                            bluestained wood without making the final
                                                                  product too dark.



Finishes for        Clear finishes are best at enhancing or       Some people find the bluestain visually
enhancing bluestain highlighting the bluestain.                   appealing.




Finish adhesion        No difference between bluestained and      No changes required in the use of stains,
                       non-bluestained wood.                      toners and glazes.
Test details
Over 500 8’,10’ and 12’ pieces of lodgepole pine 2x4              ing quality was done using the block shear test by
or 2x6 lumber were collected from 14 B.C. interior                compression loading, in accordance with ASTM and
sawmills for these tests.                                         other standards.

The evaluation of mechanical properties involved                  The finish tests were limited to furniture finishes that,
clear wood tests, which are sensitive indicators of               unlike paints, do not completely hide the wood’s
any potential impact of bluestain on performance of               natural appearance. A variety of stain, toner and
lumber. Full-size lumber may contain knots, sloped                glaze finishes were applied to the samples, alone
grain and so forth, all of which are more critical                and in combination. Finish adhesion was tested us-
factors for mechanical properties outweighing any                 ing ASTM standard industry tape tests. Appearance
small effect of bluestain. Toughness (also known as               evaluations for the various finishes were subjective.
impact bending strength), stiffness (bending modu-
lus of elasticity - MOE), breaking strength (modulus
of rupture - MOR), and the parallel-to-grain lateral
resistance of the truss plate teeth in tension were
all tested according to appropriate ASTM or CSA
standards.

There is no standard test for dimensional stability
                                                                 More Information
and checking of lumber in service caused by re-                   Tony Byrne, Research Scientist
peated wetting and drying. Forintek has developed                 Durability and Protection Group - Western Division
and regularly uses its own accelerated wetting/drying             Tel: (604) 222-5650 / Fax: (604) 222-5690
protocol and assessment procedure. Various mea-                   byrne@van.forintek.ca
sures of how far off “true” the lumber was (bow,
crook, cup, twist), check length and check width                  Details on this work are available in several Forintek reports. For informa-
were measured, and appearance of the checks was                   tion on acquiring Forintek reports, please consult our web site or phone our
                                                                  library in the Western Laboratory.
visually assessed and assigned a rating.

Permeability to liquid was tested in both simple soak-
ing and pressure treatment. The wood preservative
chromated copper arsenate (CCA) was used as a                     This document is available in Japanese Translation.
tracer, since permeability characteristics are impor-
tant to the wood treatment process. An additional
benefit of CCA as a tracer is that it stops moving
into the wood immediately upon completion of the
soak or pressure process. Uptake and retention were
measured for all samples. Before and after weights
were also measured.

The glue joint tests were conducted to determine
performance for typical applications in both struc-
tural and non-structural uses. To simulate a non-
structural application such as furniture, panels were
made using radio frequency-curable polyvinyl ac-
etate (PVA) adhesive. For an example of a structural
application such as glulam, pieces were joined using
phenol resorcinol formaldehyde (PRF). The integrity
of the glue joints was tested using the vacuum pres-
sure delamination test, and assessment of bond-




Forintek Canada Corp. acknowledges the assistance provided by the Province of British Columbia,
through the Forestry Innovation Investment Program. Forintek Canada Corp., would like to thank its
industry members, Natural Resources Canada (Canadian Forest Service), and the Provinces of British
Columbia, Alberta, Saskatchewan, Quebec, New Brunswick, Nova Scotia, and Newfoundland and
Labrador, for their guidance and financial support for this research.

				
DOCUMENT INFO